%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-4-22 on page II-172 in "mathtools, interval --- Properly spaced intervals".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3examargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{108.0pt}

%StartShownPreambleCommands
\usepackage{mathtools} \DeclarePairedDelimiter\closed{[}{]}
\DeclarePairedDelimiter\open{]}{[}\DeclarePairedDelimiter\ropen{[}{[}
\DeclarePairedDelimiter\lopen{]}{]}
%StopShownPreambleCommands

\begin{document}
\begin{gather*}
 \ropen{a,d}=\closed{a,b} + \lopen{b,c} + \dotsb \\[3pt]
 \open{\frac{a}{b}} \approx \open*{\frac{a}{b}}
                    \neq    \closed[\Bigg]{x}
\end{gather*}
\end{document}
